A process of this type is prior art in German published patent application DE 198 40 841 A1. A cold glue is applied as an adhesive to a limited area on the flat blank. The ends of the blank are glued together so that a tube is formed. This tube is slid in the form of an outer sleeve onto a pre-fabricated inner cup. Due to the stability of the tube-shaped prefabricated outer sleeve, an essentially ring-shaped air space can be formed between the outer sleeve and the inner sleeve of the cup, whereby the outer sleeve and the inner sleeve do not come into contact along the air space. The thickness of the essentially ring-shaped air space can be increased due to a discontinuous widening in the upper area of the inner sleeve, so that the insulation effect of the cup is improved.
By using cold glue as an adhesive for joining the ends of the blank of the outer sleeve, the outer sleeve can be made from a very cost-effective paper material. The blanks for the outer sleeve can consist of a single-layered paper material without additional plastic coating. In contrast to the inner cup, whose paper material comprises a plastic coating on the side forming the inner space, the outer sleeve does not come into contact with the liquid poured into the cup. A non-coated paper material is therefore sufficient for achieving the isolation effect of the double-walled cup.
The gluing of the ends of the blanks with cold glue limits the working speed of the manufacturing apparatus, as cold glue requires a relatively long time before it sets. As a result, the ends of the blank must remain pressed together for a relatively long time, in order to prevent the adhesive attachment from dissolving. In addition, the processing of cold glue is complex, as cold glue often exhibits fluctuations in viscosity, which prevents an exact dosage of the amount of glue applied. Excessive glue application results in contamination of the production machine, so that the machine often has to be stopped for cleaning.